1. Field of the Invention
This invention relates to shaped explosive charges, and in particular to a liner material used in shaped charges, such as those used in oil and gas wells.
2. Description of the Prior Art
Shaped charges for use in oil and gas well perforation and retrieval operations typically will consist of a casing which houses a quantity of explosive and a liner formed from a compressed-powder metal mixture. Materials used for such liners are well known and include copper, graphite, tungsten, lead, nickel and tin. The purpose of these metals is to allow a reasonably homogeneous mixture with specific properties. When formed under load into a liner, the density and symmetry of the liner can be controlled. By varying the material components, i.e. the material percentages in the matrix, the performance can be controlled.
Over the last few years, the tendency has been to use increasing amounts of tungsten (W) in the mixture to achieve higher density jets that penetrate deeper. One of the problems, however, with these denser powdered metal mixes, is the tendency to cause xe2x80x9csluggingxe2x80x9d or blockage of the perforation tunnel. This slugging limits the flow of hydrocarbons through the perforation tunnel and into the well bore for recovery. Slugging is attributed to a re-agglomeration of some of the liner materials during the formation of the jet. This can be from the jet itself or the after-jet, known as a xe2x80x9cslugxe2x80x9d or xe2x80x9ccarrot.xe2x80x9d The higher the density of the liner the more the likelihood of this phenomenon occurring. Therefore those mixtures with highest amounts of wolfram and other high density metals tend to produce the most slugging.
What is therefore needed is a liner material for a shaped charge with a high density to achieve maximum formation penetration, yet which reduces or eliminates those problems associated with prior art liner materials, such as slugging.
An object of the present invention is therefore to provide a means of making a high density charge lining without the disadvantages of slug formation.
Another object of the present invention is to provided a charge liner material comprising at least molybdenum (Mo) and other materials of higher density such as tungsten (W).
Yet another object of the present invention is to provide an improved shaped-charge for forming perforations in a wellbore.
These objects are achieved by providing a liner material for use in a shaped explosive charge, such as those used in oil and gas wells for perforating formations surrounding the borehole of the well. The liner material is formed from a powdered metal mixture that contains molybdenum. The metal mixture may further contain tungsten and other powdered metals. In one embodiment the liner material contains an amount of molybdenum of between about 0.5% to 25% by weight of the metal mixture, with tungsten making up between about 40% to 85% by weight of the metal mixture. The mixture may also contain graphite.
The liner may be formed in a shaped charge having a casing. The casing has a casing wall and a hollow interior. The liner is positioned within the interior of the casing, and an explosive material is disposed within the interior of the casing between the casing wall and the liner. The liner may be formed in a generally conical configuration.
Additional objects, features and advantages will be apparent in the written description which follows.